This invention generally relates to lithographic plates of the ultra high speed variety, especially those that are fast enough to be suitably exposed by a laser beam. More particularly, the present invention is directed to improvements in the manufacturing and processing of plates through the use of an extraction technique and also to the ultra high speed plates produced thereby which have an exceedingly thin layer of diazonium compound or diazonium resin that is generally uniformly located on the plate, which layer is capable of satisfactory imaging by a short time exposure such as that provided by a laser beam or such as that practiced when one or more exposures of short duration are proceded with. It is generally preferred that the diazo layer be overcoated with a polymer layer and that diazo extraction be carried out through such polymer overlayer.
Presensitized plates exhibiting very rapid photospeeds are known and include plates having a diazonium compound or diazonium resin layer overplated with photopolymer overcoatings, this type of plate being described, for example, in Thomas et al U.S. Pat. Nos. 3,808,004 and 4,133,685, the disclosures thereof being incorporated by reference hereinto. Although these plates do exhibit very rapid photospeeds, such speeds typically are not adequate for use within systems that include exposure steps that are of the laser speed variety or are similar in overall exposure time to laser systems, referred to herein as ultra high speed systems.
Ultra high speed exposures may be accomplished, for example, with conventional lithographic plate exposure units by exposing the plates for a time period that is extremely short when compared with that needed for adequate exposure in the particular unit of lithographic plates that are not of an ultra high speed character. Typically, an ultra high speed plate will be satisfactorily imaged with an exposure time that is between about 4 to 10 times faster than the usual exposure time needed for the particular type of unit. Such conventional exposure units generally utilize actinic energy sources that are of a broad-band variety which encompass both visible and ultraviolet and/or infrared wavelengths, for example as generated by a mercury vapor lamp, a pulsed xenon lamp, or a rare earth metal halide doped mercury lamp. Presensitized plates usually will be responsive to energy across a range of wavelengths that is of a breadth on the order of the broad-band variety output of these conventional exposure units.
With laser exposures, the exposures are often of about the same general magnitude as exposures for ultra high speed applications of conventional exposure units, but laser systems will provide a much narrower, usually a single wavelength, spectral bandwidth and a much greater light intensity than those developed by the conventional exposure units, and will typically be applied in an overlapping, scanning manner in order to expose the entire plate and avoid the formation of scan lines on the exposed plates. Because of differences such as these, it is not a foregone conclusion that a plate suitable for conventional exposure will respond to a laser exposure source in the same manner or as satisfactorily as it will respond to a conventional unit. An important difference in observed response is the step wedge transmission pattern that is exhibited by a laser exposure compared with a conventional exposure, which difference is due in part to the fact that conventional step wedges are intended for exposure by conventional light sources. Roughly speaking, a step 2 image formed by a laser exposure source would designate an exposure as satisfactory as a step 5 image formed by a conventional exposure source. For example, a step 2 image made by an ultraviolet laser represents a laser transmission of about 40%, while a step 5 image made by a particular conventional exposure source having visible bands represents a transmission of about 25 to 30% of that conventional source.
Ultra high speed exposures have certain advantages that cannot be attained by conventional plates, even presensitized plates of rapid photospeeds. Advantages such as cost, labor and time savings and the ability to be adapted for advanced systems, including facsimile transmission and computer printing are discussed in "Laser Platemaking Systems For the Printing Industry", R. E. Amtower, presented at Electro-.ptics/Laser Conference and Exhibition, New York, September, 1976; and "Computers To Plates-A Realty", L. G. Larson, presented at PIRA Symposium, London, 1977.
Lithographic plates of the non-presensitized, wipe-on variety or of the electrostatic variety have been produced for use in plate making systems that utilize exposure methods and devices of the laser type. Electrostatic laser-speed lithographic plates are not of the diazo type, and they are much more expensive than diazo or photopolymer plates.
Lithographic plates of the wipe-on type that exhibit photospeeds suitable for ultra high speed uses retain the typical disadvantages of conventional wipe-on plates, including relatively short shelf life properties, poor roll up attributes, undesirable physical appearance of the plates, frequency of unsuitable processing by the user and resultant waste, difficulty of achieving a uniform coating to avoid inferior dot structure, lower overall printing quality largely due to a typically low number of line screens. Typically, special diazo solutions must be used when ultra high speed wipe-on plates are prepared, and such solutions must be applied in a very thin layer just prior to exposure, whether application be by a skilled operator or by a wipe-on solution applicator machine. Wipe-on plates cannot be put into direct use, but must be first processed through the wiping opertion.
The present invention relates to presensitized diazo plates that are satisfactory for use within ultra high speed systems, such as: those requiring projection plates, where an image is projected from a slide onto an offset plate; camera back plates, where an offset plate is used to take an image in a camera and in which a film step is eliminated; those including step and repeat and work, where many repetitive exposures must be made; systems incorporating laser exposures for facsimile transmissions; computer to press systems that require laser speed plate making; uses for preparing oversized plates, typically utilizing low intensity light sources; or use in newspaper printing where inexpensive ink and paper are used and lint build up is a serious problem. Plates according to this invention are suitable for high volume reproduction operations such as that needed for newspapers, directories, business forms, multiple listings, and the like.
Presensitized diazo plates according to this invention exhibit the superior run length and roll up properties typically associated with presensitized lithographic diazo plates while also exhibiting photospeeds suitable for ultra high speed exposure techniques. These plates have an exceedingly thin, yet generally uniform diazo layer that is residual diazonium compound or diazonium resin retained on the plate after extraction of substantially all of an initial diazo layer from off of the plate substrate. In an important aspect of the method of this invention, a sensitizing or extracting agent is put into contact with a plate having a presensitized layer including a diazonium compound or diazonium resin, and the sensitizing or extracting agent, which is a liquid that will solubilize the diazo material but will not solubilize, soften, damage, swell, or otherwise adversely affect the rest of the plate that preferably includes a photopolymer, is subsequently removed from the plate together with a substantial amount of the diazonium compound or diazonium resin.
It is a general object of this invention to provide an improved ultra high speed lithographic plate.
Another object of the present invention is to provide a product and processes for making a presensitized lithographic plate of the ultra high speed variety suitable for use in systems that incorporate laser exposure of plates.
Another object of this invention is to provide an improved presensitized lithographic plate and methods for preparing same, which plate is suitable for use in projecting an image from a slide onto an offset plate.
Another object of this invention is to provide an improved presensitized lithographic plate and method for making same, the plate being suitable for use in taking an image in a camera, whereby a film step is eliminated.
Another object of this invention is a presensitized lithographic plate and method for making same, which plate is suitable for step and repeat work when many repetitive exposures must be made.
Another object of the present invention is to provide an improved lithographic plate and method for making same that is suitable for exposure by low intensity light sources, especially when the plates are oversized.
Another object of this invention is an improved presensitized lithographic plate and method for making same that is suitable for use within facsimile transmissions, especially those in conjunction with computer to plate composing and printing operations for high volume and remote printing using scanning laser systems.
These and other objects of this invention will be apparent from the following further detailed description thereof.
Ultra high speed lithographic plates according to this invention include a substrate that is suitable for accepting, with good adhesion, a diazo substance, the ultra high speed plate further including an extremely thin layer of such diazo substance, said layer being adequately adhered to the substrate. Preferably, a polymeric substance is also included on the substrate, such polymer being provided for the purpose of protecting the diazonium compound or diazonium resin and/or enhancing its photospeed.
Substrates suitable for the present invention can be of any type that will be strongly adhered to by a diazo substance, which adhesion can be enhanced by chemical means, substrates of paper, plastic or metal being useful. Diazo to substrate adhesion can be increased by a substrate surface exhibiting surface roughness such as a grained surface formed by ball graining, chemical graining, brush graining or the like. Surface hardness of the substrate and enhanced diazo adhesion thereto can be brought about by anodizing. In addition, the substrate may be subjected to steps such as etching, coating or rinsing prior to diazo addition. Whatever substrate treatment is used, it is important to good adhesion that the plate be clean and free of oil.
Almost any diazonium compound or diazonium resin suitably functions as the diazo layer, whether the diazo be water soluble or solvent soluble, it being an important aspect of this invention that the diazonium compound or diazonium resin exhibit at least a minimal solubility within the extracting agent of this invention. Typical diazonium compound or diazonium resin are described in U.S. Pat. Nos. 2,100,063, 2,667,415, 2,679,498 and 2,958,599. An example of a diazo resin of the negative-working type is prepared by condensing paraformaldehyde with p-diazo-diphenylamine sulfate in the manner set forth in U.S. Pat. No. 2,100,063. The diazonium compound or diazonium resin, which may be applied to the substrate by any means, such as by the well-known procedures of dipping, spraying, roller coating, brushing, or the like, can be one or more water-soluble or solvent-soluble diazo substances applied in one or more layers of only diazonium compound or diazonium resin or of a combination of diazonium compound or diazonium resin and another component, such as a polymeric substance.
Plates according to this invention have an exceptionally thin diazo layer that is of a residual thickness remaining on the plate substrate after extraction of diazonium compound or diazonium resin from a diazo layer of a thickness greater than this residual thickness, the residual thickness believed to be in the general nature of a substantially monomolecular layer that is extensive enough to provide a diazo layer that, although it can exhibit discontinuities, it will form a printed image that is continous to the unaided eye. The residual thickness material is thick enough to provide for an adequate image formation and to cause polymer, if present, to cross-link and adhere to the plate surface upon exposure, but being thin enough to bring about ultra high speeds characteristic of this invention. While it is presently believed that the residual thickness diazo layer of plates according to this invention is no greater than about 0.05 mg./sq.ft, a method for actual measurement in this regard is not known at present; visible spectroscope measurements made in the near ultraviolet range on washing solutions applied to plates having a residual thickness diazonium compound or diazonium resin do not detect the presence of any diazo material.
Polymeric substances are preferably included on the substrate as a layer that is over or that includes the diazonium compound or diazonium resin, the layer being thin enough to permit passage of the diazonium compound or diazonium resin out of or through such layer by operation of the extracting agent of this invention, a typical polymer layer being of a thickness no greater than about 200 mg of polymer per square foot of substrate surface area, typically between 5 and 120 mg, the preferred thickness varying with the coverage characteristics of the particular polymer and with the roughness of the substrate, a usual preferred range being between about 10 and about 100 mg/sq.ft. The polymer should be of a thickness such that it is not completely continuous to the extent that the extracting agent can pull substantially all of the diazonium compound or diazonium resin therethrough, and it is believed that such a property is enhanced somewhat when the substrate is grained, unetched, or otherwise exhibits surface irregularities so that the polymer layer thereover is more likely to have discontinuities for enhancing passage of diazonium compound or diazonium resin therethrough. In a very general sense, the polymer layer can be thought of as being microscopically pin-holed or cracked, the pin-holding in general being brought about by a combination of the thickness of the polymer layer, the roughness of the substrate surface, and perhaps most importantly the drying properties of the particular polymer, pin-holing being more likely to develop when the applied polymer formulation includes a solvent that escapes through the polymer on setting and when relatively fast or harsh drying conditions were present.
When the polymeric substances are included on plates according to this invention, they provide protection for the extremely thin diazo layer, they serve as an advantageous medium through which the diazonium compound or diazonium resin are extracted, they can provide coloration when dyes or pigments are included, and preferably they also are of a type that will even more greatly increase the photospeed of the extremely thin diazo layer. Polymeric substances include resinous materials that provide little or no photospeed enhancement or photopolymers such as those described in U.S. Pat. No. 3,808,004, which can be generally thought of as cinnamoylated photopolymers. These polymeric materials include phenoxy cinnamate photopolymers, polyvinyl cinnamate photopolymers, bisphenol-A fumarate polyester cinnamate photopolymers, polycarbonate cinnamate photopolymers, polyurethane cinnamate photopolymers, photopolymeric alkyd resins, sensitized aryl allyl ester polymers as discussed in U.S. Pat. No. 3,462,267, polycarboxylic acid polymers as discussed in U.S. Pat. No. 3,136,636, isocyanate-modified polyfunctional ethylenically unsaturated polymers as discussed in U.S. Pat. No. 3,840,369, polymers of o-nitro-carbinol esters of ethylenically unsaturated carboxylic acids as discussed in U.S. Pat. No. 3,849,137, and polyvinylformal resins, vinyl polymers, epoxy resins, alkyd resins, polyamide resins, phenolaldehyde resins, ureaaldehyde resins, cellulose acetate butyrate, polyalkylene-polysulfide resins, and silicon containing resins as discussed in U.S. Pat. No. 3,136,637.
Optionally included on plates according to this invention are stabilizers, which are most conveniently added with the extracting agent at up to 2 weight percent of the composition, for enhancing the shelf life of these plates after their photospeed has been significantly enhanced by thinning the diazo layer. Stabilizers include zinc chloride, phosphoric acid, hydrochloric acid, acetic acid, citric acid, sulfuric acid, tartaric acid, p-toluene sulfonic acid, fluoboric acid, or combinations thereof, or the like.
In proceeding with the plate-modifying method according to this invention, an important aspect thereof is the step of treating a plate having a substrate and a diazo layer with an extracting agent in order to remove substantially all of the diazo layer to thereby leave an exceedingly thin, residual thickness layer of diazonium compound or diazonium resin, which exceedingly thin layer exhibits ultra high photospeeds that are suitable for laser-type operations. In one aspect of this invention, presensitized diazo plates are thus treated in order to transform them from conventional speed or relatively high speed plates into ultra high speed plates. Typically, plates so produced will be fast enough to be adequately exposed by ultraviolet laser unit when supplied with on the order of about 10 millijoules of laser energy per square centimeter of plate surface.
More particularly, the treatment step or procedure according to this invention includes applying a liquid extracting agent to a presensitized diazo lithographic plate in order to form the exceedingly thin, residual thickness diazo layer by extracting off of the plate surface substantially all of the diazonium compound or diazonium resin until what is believed to be greater than about 90, and more probably greater than approximately 99 weight percent of the initial diazo layer has been extracted, and then removing the agent and extraced diazonium compound or diazonium resin from the surface of the plate. Usually, carrying out the treatment step a plurality of times on each plate will enhance the photospeed to a greater extent than does a single treatment step.
In its simplest form, the step of applying the extracting agent to the plate is one of contacting the plate with the liquid agent to extract the diazo, and the removing step is one of permitting the plate to dry in order to terminate extraction prior to use of the plate. Other applying techniques can include dipping or immersing the plate within a container or tray of the extracting agent, or by passing over the plate a sponge containing the extracting agent, although a more controlled applying procedure has been found to be brought about by applying the agent with a developing pad or the like, such as a rubberbacked, short-brushed plush, or synthetic fur of relatively short length, on the order of 1/8 inch.
Especially suitable for the applying and removing steps is any operation which puts the extracting agent liquid into contact with the total plate surface area, permits excess liquid to drain off the plate, and physically removes by scraping, wiping or the like substantially all of the remaining diazo-containing extracting liquid from off of the plate, after which the plate is permitted to dry. An especially suitable combination for completing the treatment includes dipping the plate within a tray or other container of extracting agent, holding the liquid on the surface for a length of time adequate to extract the diazo, and then wiping the surface with a squeegee or the like. Typical holding times generally are not much longer than about 3 minutes, usually between about 2 seconds and 2 minutes, preferably between about 5 and 60 seconds, while an especially preferred holding time for many presensitized diazo plate and extracting agent combinations is between about 10 and 45 seconds. Particularly suitable for carrying out substantially all of these steps of the treating procedure is the use of a conventional mechanical plate wipe-on apparatus which automatically immerses, drains, and wipes the plates, making them ready for ultra high speed uses after the plates dry.
Optionally included within the treating procedure can be a rinsing step, which enhances removal of the diazo-containing extracting agent from the plate by passing a rinsing agent over the plate. Typical rinsing agents are aqueous liquids, such as deionized water or tap water, and a typical rinsing step will pass a supply of rinsing agent over the surface of the presensitized ultra high speed diazo lithographic plate. When a stabilizer is to be included, it can advantageously be added to the rinsing agent.
By this treating procedure, a solubilizing substance is utilized as an extracting agent and has the effectiveness of an ultra high speed sensitizing agent. For a solubilizing substance to be a suitable extracting or sensitizing agent, it should be one in which the diazonium compound or diazonium resin is highly, either totally or partially, soluble while at the same time being a substance that will not significantly solubilize, soften, damage, swell or otherwise adversely affect the rest of the plate, particularly the photopolymer when present. Solubilizing substances include tap water, deionized water, aqueous solutions or blends including surfactants, solvents and/or other acidic, basic or salt additives. Typically, organic solvents by themselves or in high concentrations are useful only when the diazo material is of the solvent-soluble, as opposed to the water-soluble type for which the other exemplified solubilizing substances are most suitable. The aqueous solutions or blends can include: at least about 30 weight % water, preferably at least 50%, often most suitably at least 75% water; up to 1% surfactant, preferably 0.001-0.1%; and up to 70 weight % solvent, preferably no more than 25%. When present, the surfactants and solvents lower the surface tension within the system to allow the solubilizing substance or extracting agent to wet and to penetrate the polymeric substance more readily, while at the same time facilitating a more uniform and what is believed to be a more rapid wash out of the diazonium compound or diazonium resins. The other additives are included to add dissolved minerals to the system, to adjust the pH, and/or to assist in stabilizing the ultra high speed plates once they are sensitized.
Exemplary surfactants include high to moderately low molecular weight bis-(polyethoxylated) poly (propylene glycol) hydrophilic nonionic surfactants, cationic surfactants such as a 50/50 mixture of water and methyl dodecyl benzyl xylene bis-trimethyl ammonium chloride, and anionic surfactants such as sodium dioctyl sulfosuccinate, or combinations thereof. Solvents include alcohols such as ethanol, n-propanol, isopropanol and diacetone alcohol; 2-methoxyethanol; 2-ethoxyethanol; glycols such as ethylene glycol or propylene glycol; polymer solvents, if at especially low concentrations, such as 2-ethoxyethyl acetate, dioxane or tetrahydrofuran; and combinations thereof. Acidic, basic or salt other additives include phosphoric acid, citric acid, acetic acid, ammonia, magnesium carbonate, calcium carbonate, sodium chloride, ammonium acetate, sodium bisulfate, sodium bisulfite, magnesium nitrate, sodium bicarbonate, sodium carbonate, citric acid monhydrate, anhydrous sodium acetate, sodium acetate trihydrate, 10.degree. Be gum arabic solution, zinc chloride, hydrochloric acid, sulfuric acid, tartaric acid, p-toluene sulfonic acid, fluoboric acid, and combinations thereof. The pH of the extracting agent composition generally can range between 1 and 12, preferably not above about 7, and, especially when shelf-stability is to be enhanced, between 2 and 6. When the higher pH compositions are used, the overall alkalinity imparted thereby should be low enough to be overcome by the dominantly acidic diazonium compound or diazonium resin.
The plate making method according to this invention includes coating a plate having a backing of paper, plastic sheet, aluminum, zinc, copper, other metal or the like. Preferably, such backing is processed in order to form a treated substrate enhanced in its ability to adhere diazo materials thereto, such as by rendering the surface hydrophilic by any one of various possible combinations of steps, including graining, etching, anodizing, rinsing, and coating with a subbase or combination of subbases such as a phytic acid subbase as described in U.S. Pat. No. 3,307,951, a melamine-formaldehyde condensation resin overcoated with a poly-acrylamide as described in U.S. Pat. No. 3,073,723, a ureaformaldehyde subbase as in U.S. Pat. No. 3,136,636, a titanium ortho ester subbase of U.S. Pat. No. 3,231,376, a silane-acrylic subbase of U.S. Pat. No. 3,163,534, a silicate subbase of U.S. Pat. No. 2,714,066, the subbase of U.S. Pat. No. 3,261,285, a gelatin, a polyacrylic acid and water-soluble salts thereof, a polymethacrylic acid and water soluble salts thereof, a carboxy-methyl cellulose, a carboxymethyl hydroxyethyl cellulose, a titanate, a modified resin of urea-formaldehyde and melamine-formaldehyde, a polyvinyl alcohol, a ferrocyanide of sodium, potassium or ammonium, a bichromate of sodium, potassium or ammonium, or, when the substrate is a metal, an oxide thereof.
A layer containing a diazonium compound or diazonium resin is coated onto the backing or the treated substrate, this layer being substantially entirely a single diazo or a combination of different diazo materials, although optionally, the diazonium compounds or diazonium resins material may be applied in combination with a polymeric substance, the thickness of the applied diazonium compound or diazonium resin coating layer being between about 1 and about 10 mg, preferably between about 3 and about 8 mg, of diazo per square foot of substrate or backing surface area, although the diazo layer could be as high as about 50 mg. per square foot.
Preferably, the diazo layer is next overcoated with a layer of polymeric substance which exhibits protective properties and which in addition preferably exhibits properties whereby photospeed increase is realized, any such polymeric substance layer being of a thickness that permits removal of diazo resin therethrough, such a thickness typically being no more than approximately 120 mg of polymer for each square foot of plate surface area.
Thereafter, the treating procedure according to this invention is proceeded with, during which the solubilizing or extracting agent that performs as an ultra high speed sensitizing agent according to this invention is applied to and removed from the presensitized diazo lithographic plate. After the thus prepared plate is dry, it is suitable for use in ultra high speed systems.
Ultra high speed exposures may be attained by non-laser units at exposure times that are significantly shorter than needed for plates that are not of the ultra high speed variety. Laser exposure systems are also suitable for satisfactorily exposing the ultra high speed plates of this invention, possible laser types being dependent upon the particular diazonium compound or diazonium resin, representative types being ultraviolet lasers such as UV argon and UV krypton whether water-cooled or air-cooled; visible lasers such as argon visible or krypton violet; and infra-red or near infra-red lasers. Typical laser scanning systems will scan an entire newspaper-sized plate in approximately one minute.